The invention relates to a valve device with a movable valve element, in particular for controlling the gas flow in an internal combustion engine.
Valve devices are required in various sectors of industry for controlling flow of a gaseous or liquid medium. Valve devices used in internal combustion engines of motor vehicles are considered below, but without the invention being restricted to them.
Valve devices of internal combustion engines serve for controlling the inlet of combustion air or outlet of the exhaust gases. Typically, a movable valve element in the form of a valve tappet is moved back and forth linearly between an open position and a closed position. According to the prior art, the force necessary for executing this movement may be generated, for example, by camshafts or by means of electromagnetic coils or hydraulic or pneumatic actuators. When known actuators are used, however, there is still a need for improvement with regard to compactness and efficiency.
An important aim of this improvement is that, when ideal valves are used, the performance of an internal combustion engine can be regulated, without a throttle valve being employed, solely by the time control or timing of the valve opening and by the valve stroke.
Against this background, an advantage of the present invention is that it provides a valve device which is suitable for use in internal combustion engines allowing efficient and flexible valve control.
The valve device according to the invention with a movable valve element has at least one artificial muscle element coupled to the valve element. In this context, the term xe2x80x9ccouplingxe2x80x9d may also mean a physical identity of valve element and muscle element.
Artificial elements are novel actuators which in their properties are similar to or simulate natural musculature. A particular characteristic of artificial muscles is force generation taking place in the volume as a result of atomic or molecular interactions. Often, in a similar way to natural muscles, artificial muscles consist of soft material of variable form. Force generation in known artificial muscles may be based, for example, on electrostatic forces of attraction, on the piezo-electric effect, on ultrasound generation, on a form memory of materials, on ion exchange, on an extension of carbon nanotubes and/or on the incorporation of hydrogen into metal hydrides. Depending on the active principle, artificial muscles may be produced from polymers, in particular polymer gels, from ferroelectric substances, from silicon, from alloys with a form memory or the like. A detailed description of various types of artificial muscles is found, for example, in EP 0 924 033 A2, US 2002/0026794 A1, and U.S. Pat. No. 6,109,852.
Preferably, the valve device described makes use of artificial muscle elements of this type which can be controlled by means of an electrical signal. In particular, the mechanical energy generated by the muscle element can originate from the electrical energy of the signal. Electrically-controlled artificial muscle elements have the advantage that they are compatible with the conventional control technology of an internal combustion engine.
In one embodiment of a valve device, artificial muscle elements are used which can actively contract, actively expand and/or actively change their form, such as, for example, their curvature. Artificial muscle elements which can actively generate a force in two opposite directions can in this case even individually induce the entire movement of the valve element. By contrast, when an artificial muscle element can generate an active force in only one direction, it has to be supplemented by a force generator which is active in the opposite direction, for example a further artificial muscle elements, to make the valve element controllable in the opening and closing directions.
As already explained, in principle, all types of artificial muscle elements can be used for the proposed valve device. In one embodiment, artificial muscle elements based on the interaction of carbon nanotubes are used. Artificial muscle elements of this type are distinguished by a high heat resistance of up to 1000xc2x0 C. Furthermore, muscle elements of this type can be controlled and expanded by electrical energy (cf. Science of May 21, 1999). A further preferred type of artificial muscle is based on polymer gels (cf. Low, L. W.; Madou, M. J. xe2x80x9cMicroactuators towards microvalves for controlled drug deliveryxe2x80x9d, Sensors and Actuators B: Chemical, 67 (1-2) (2000) pp. 149-160).
There are numerous possibilities for the structural configuration of the valve element. So that the changes to existing engines are minimal, many known structural elements are adopted. In particular, the valve element may be formed by a valve tappet which is mounted with displacement movability and to which the artificial muscle element is coupled directly or indirectly, that is to say via intermediate components, such as, for example, rocker or drag levers.
According to a special embodiment of the abovementioned valve device with a valve tappet, the latter is coupled to a prestressing element, for example to a helical spring. The prestressing element can generate a force in one direction of movement of the valve tappet. The artificial muscle element then only has to be capable of generating a force in the opposite direction to make the valve element as a whole controllable.
In another embodiment of the valve device with a valve tappet, the latter is coupled to a gas pressure chamber in such a way that a pressure rise in the gas pressure chamber causes a movement of the valve tappet. By the pressure in the gas pressure chamber, therefore, a force can actively be exerted on the valve tappet.
Preferably, in the last-mentioned embodiment with a gas pressure chamber, the walls of the gas pressure chamber are formed completely or at least partially by the artificial muscle element. This double function of the artificial muscle element contributes to a more compact construction which saves material and allows direct interaction between the artificial muscle element and the pressure in the gas pressure chamber.
In another development of the valve device, the valve element is formed by a pivotally movable flap which, depending on the set angle, can open or close a throughflow orifice. In particular, in this case, a plurality of such flaps may also interact jointly to control the throughflow orifice. A valve element of this type with a plurality of flaps is more robust against total failure and can be actuated more quickly, since a plurality of flaps simultaneously execute a travel into the opening or closing position.
Furthermore, it is possible to have embodiments of the valve device in which the valve element is formed by the artificial muscle element itself, that is to say is physically identical to it. In this case, the artificial muscle element may be arranged, for example, in a passage and close or open the latter as a result of an active change in form or in volume.
The above advantages and other advantages, objects, and features of the present invention will be readily apparent from the following detailed description of the preferred embodiments when taken in connection with the accompanying drawings.